1. Field of the Invention
The preferred embodiment of the present invention is generally related to a fuel injector and, more particularly, to a fuel injector which uses piezoelectric devices to both pressurize the fuel and to control a valve by which the pressurized fuel is released through an outlet port of the fuel injector.
2. Description of the Prior Art
Many different types of fuel injectors are known to those skilled in the art. Piezoelectric devices, such as those devices using a lead zirconate titanate element are also known to those skilled in the art. In certain applications, piezoceramic elements made of a lead zirconate titanate (PZT) have been used to actuate a movable valve.
U.S. Pat. No. 6,291,929, which issued to Heinz et al. on Sep. 18, 2001, describes a piezoelectric actuator. The invention relates to a piezoelectric actuator, in particular for actuating control valves or injection valves in internal combustion engines of motor vehicles, having a piezoelectric actuator body in the form of a multi-layer laminate of stacked layers of piezoelectric material and metal or electrically conductive layers, acting as electrodes, located between them, in which one of the face ends of the actuator body is fixed to a stationary metal actuator base, and the other face end borders a metal retaining plate that is movable with the actuator stroke.
U.S. Pat. No. 5,094,429, which issued to Dostert on Mar. 10, 1992, describes a valve having a piezoelectric drive. A lever mechanism is provided with a prescribed lever ratio and includes a resilient steel fork for the amplitude transformation of the excursion of a piezoceramic element operating as a piezoelectric actuator, a valve lifter connected at one end to a deflectable end of the steel fork and at the other end to a valve needle of a fuel injector valve.
U.S. patent application Ser. No. 10/462,194, which was filed on Jun. 16, 2003, by Gatecliff et al., describes a piezoelectric valve actuation system. The system is intended for use in an internal combustion engine and includes a piezoelectric driver in the form of a prestressed wafer or strip including a layer of piezoceramic material such as lead zirconate titanate (PZT). The driver has a central portion which includes an aperture for direct engagement with a valve stem so that the valve is moved between open and closed positions directly by the piezoelectric driver. The piezoelectric driver can have end portions which attach to the engine cylinder head proximate the valve location. The piezoelectric actuator is driven by an electronic control module (ECM) providing electrical signals to control valve operation based various engine parameters along with user input.
U.S. Pat. No. 5,816,780, which issued to Bishop et al. on Oct. 6, 1998, describes a piezoelectrically actuated fluid pump. The pump includes a pump housing, a pump chamber, inlet and outlet ports for communicating the pump chamber with the exterior of the pump housing, valves for opening and closing the ports, two prestressed piezoelectric diaphragm members which are self-actuated, and a power source. The diaphragm members include a prestressed piezoelectric element which is durable, inexpensive and lightweight as compared with prior diaphragm pumps of comparable discharge capacity, and is actuated via electrical signals from an outside power source.
U.S. Pat. No. 6,042,345, which issued to Bishop et al. on Mar. 28, 2000, describes a piezoelectrically actuated fluid pump. The diaphragm members of the pump include a prestressed piezoelectric element which is durable and lightweight.
U.S. Pat. No. 4,927,084, which issued to Brandner et al. on May 22, 1990, describes a fuel injection valve. A reciprocable valving element is movable from closed to open positions by a piezoceramic moving unit having at least to flexural resonators in the form of laminated packages of metallic carriers, ceramic layers and foil shaped and/or ring shaped conductors connected to the poles of an energy source in such a way that energization entails deformation of packages in opposite directions, namely the deformed packages have confronting concave or convex sides. This increases the distance which is covered by the valving element in response to energization of the packages.
U.S. Pat. No. 4,437,644, which issued to Wilmers on Mar. 20, 1984, describes an electrically operable valve. The invention relates to valves for use in fuel injection systems for internal combustion engines. The valve has a housing having a valve seat, and receiving a valve body which can be raised from the valve seat in accordance with a variation in dimension of magnetostrictional device or a piezoceramic device caused by a current flow in the device. The valve body is spring loaded in a sense to close the valve and is connected via the device to a movable abutment unit which is so constituted that during the current induced variations in dimension it acts as a stationary abutment or anchorage for that end of the device which is remote from the valve body.
U.S. Pat. No. 4,593,658, which issued to Moloney on Jun. 10, 1986, describes a valve operating mechanism for internal combustion engines and like valved engines. The valve operating mechanism for an internal combustion engine comprises a piezoelectric control device arranged to control the operating movement of an engine valve in accordance with the extension of the control device and control means for controlling the electrical feed to the piezoelectric device in accordance with parameters of the engine operation fed to it.
U.S. Pat. No. 4,739,929, which issued to Brandner et al. on Apr. 26, 1988, describes a fuel injection valve. The valve has a piezoceramic valve body comprising a plurality of superposed ceramic plates each having one conductor layer on each side and voltage leads to the conductor layers. Each ceramic plate is arranged on a carrier plate. Between each unit, consisting of a ceramic plate and a carrier plate, an insulating foil is provided with conductor foils arranged on each side as conductor layers. Each insulating foil comprises two terminal lugs. Each insulating foil, in the region of a terminal lug, is laminated on one side with one conductor foil. The correlated terminal lugs are connected in each case to an electrical contact with the correlated conductor foils.
U.S. Pat. No. 4,813,601, which issued to Schwerdt et al. on Mar. 21, 1989, describes a piezoelectric control valve for controlling fuel injection valves in internal combustion engines. A piezoelectric control valve includes a hydraulic plate compensation element inside the control valve on the one side which automatically compensates for possible changes in length of the reference system as a result of piezoceramic setting actions in the piezoelectric actuator so that, at the same working stroke of the piezoelectric actuator, an identical stroke at the valve is also always ensured. A hydraulic stroke transmission inside the control valve on the other side, provides a valve stroke corresponding to a multiple of the working stroke.
U.S. Pat. No. 5,203,537, which issued to Jacobs et al. on Apr. 20, 1993, describes a piezoceramic valve actuator sandwich assembly and valve incorporating such an assembly. The valve includes a valve actuator sandwich assembly including a piezoceramic bending element flexibly bonded between two metal sheets. Flexible elastomeric sheets are bonded to outer surfaces of the metal sheets, respectively, to form the sandwich assembly. The valve includes a first supporting member which sealingly engages an outer surface of the first elastomeric sheet and a second supporting member which sealingly engages an outer surface of the second elastomeric sheet to flexibly support the valve actuator sandwich assembly between the two supporting members. The valve actuator is engageable with a valve seat to prevent flow through the valve and is deflectable away from the valve seat to allow flow through the valve. The piezoceramic bending element is isolated in the valve actuator sandwich assembly from the flow stream to prevent diffusion of low molecular weight gases through the porous ceramic and to isolate electrically active elements of the bending element from the flow stream.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
A thesis entitled “A Comprehensive Piezoceramic Actuator Review and Its Application to the Design of a Direct-Injection Fuel Injector”, which was presented by Christopher John Taylor in partial fulfillment of the requirements for the Degree Master of Science in the Graduate School of The Ohio State University, describes the technology relating to piezoceramic actuators along with a description and analysis of various characteristics of specific types of piezoceramic actuators.
A document titled “Thunder White Paper” was published in 2001 by the Face International Corporation. That White Paper, which is available on the Internet, describes the technology relating to lead zirconate titanate (PZT) piezoceramic and piezoelectricity along with illustrations showing the construction and advantages of certain devices manufactured and sold by Face International Corporation. Various application notes are also described in detail therein.
An article titled “Application Notes” was published in 2002 by Face International Corporation. This article is available on the Internet and specifically discusses an element, or component, relating to a thin layer Unimorph Ferroelectric Driver and Sensor which is commercially available from Face International Corporation under the name “THUNDER”. This paper describes the underlying technology relating to the PZT element and illustrates certain advantageous application techniques relating to using the PZT component in various applications.
It would be advantageous if a fuel injector could be made with a pressurizing portion and an actuation portion both utilizing piezoelectric elements. This type of device could advantageously control the pressurization and injection of fuel in an internal combustion engine. It could provide a reliable and durable structure for such a fuel injector.